Capacitance-detection-type proximity sensors (which are also referred to as capacitance-detection-type sensors) detect the approach of objects (objects to be detected) by measuring the change in capacitance that occurs due to the presence of human bodies or the like. Capacitance-detection-type proximity sensors can be broadly classified into two types depending on where the detection electrode is disposed.
The first type uses an appropriate method to detect and measure the capacitance (i.e., earth capacitance) that one detection electrode disposed to face an open space forms relative to the common ground potential (or common reference potential). When an object to be detected approaches the detection electrode, the capacitance changes due to the effect of the object to be detected. This change is measured in order to detect the approach of the object to be detected.
The second type measures the capacitance (i.e., inter-electrode capacitance) that is formed between two detection electrodes disposed to face each other. An object to be detected that is present between the two detection electrodes changes the inter-electrode capacitance. This change is measured in order to detect the approach of the object to be detected.
The invention disclosed, for example, in Patent Literature 1 relates to a hand dryer that uses capacitance-detection-type proximity sensors. The technology disclosed in Patent Literature 1 is such that detection electrodes are disposed near the hand insertion portion in order to detect the presence or absence of a hand inserted into the hand insertion portion and the presence or absence of a hand is detected in accordance with the change in capacitance that is generated in the detection electrodes due to the hand being inserted into the hand insertion portion.